A printing system is described in the commonly assigned patent application entitled "CONTINUOUS REFILL OF SPRING BAG RESERVOIR IN AN INK-JET SWATH PRINTER/PLOTTER" which employs off-carriage ink reservoirs connected to on-carriage print cartridges through flexible tubing. The off-carriage reservoirs continuously replenish the supply of ink in the internal reservoirs of the on-carriage print cartridges, and maintain the back pressure in a range which results in high print quality. While this system has many advantages, there are some applications in which the relatively permanent connection of the off-carriage and on-carriage reservoirs via tubing is undesirable.
A new ink delivery system (IDS) for printer/plotters has been developed, wherein the on-carriage spring reservoir of the print cartridge is only intermittently connected to the off-carriage reservoir to "take a gulp" and is then disconnected from the off-carriage reservoir. No tubing permanently connecting the on-carriage and off-carriage elements is needed. The above-referenced related applications, entitled SPACE-EFFICIENT ENCLOSURE SHAPE FOR NESTING TOGETHER A PLURALITY OF REPLACEABLE INK SUPPLY BAGS, PRINTING SYSTEM WITH SINGLE ON/OFF CONTROL VALVE FOR PERIODIC INK REPLENISHMENT OF PRINTHEAD, and APPARATUS FOR PERIODIC AUTOMATED CONNECTION OF INK SUPPLY VALVES WITH MULTIPLE PRINTHEADS, describe certain features of this new ink delivery system.
This invention optimizes the performance of this new off-carriage, take-a-gulp ink delivery system. In this type of IDS, a print cartridge that uses an internal spring to provide vacuum pressure is intermittently connected to an ink reservoir located off the scanning carriage axis. Starting with a "full" print cartridge, the printer will print a variety of plots while monitoring the amount of ink used. After a specified amount of ink has been dispensed, the carriage is moved to a refill station for ink replenishment. In the refill station, a valve is engaged into the print cartridge, thus connecting the ink reservoir to the print cartridge and opening a path for ink to flow freely. Using only the vacuum pressure present in the print cartridge, ink is "pulled" into the print cartridge from the reservoir.
Print cartridge vacuum pressure varies with the amount of ink contained in the print cartridge. Typically, low ink volume relates to high vacuum pressure and high ink volume is associated with low vacuum pressure. The vacuum pressure-ink volume curve exhibits hysteresis, in that a different vacuum pressure is realized in the print cartridge during printing (ink volume reduction) than when refilling (ink volume increase) for a given ink volume. Additionally, the refill vacuum pressure curve contains several relative peaks or "bumps" whereby several ink volumes can yield the same vacuum pressure. This poses a significant problem for this type of self regulating refill system where the flow of ink into the print cartridge stops when the vacuum pressure in the print cartridge is equal to the distance the ink reservoir is offset below the print cartridge. Thus, for a given offset distance, the print cartridge will always refill to the smallest volume that yields a pressure equal to the offset distance. These small "topped-off" refill volumes are unpredictable and often quite small (roughly half the print cartridge reservoir volume), and this is undesirable.